A rolling mill stand can have two working rolls each of which is supported directly or by an intermediate roll on a support or backup roll, the rolls of a roll pair, i.e. two complementarily functioning rolls, being axially shiftable in opposite directions and each of the rolls which are axially shiftable at least over a portion of the length of its roll body having a curved contour diverging from an axially parallel alignment, which extends over the entire length of the roll body, the contours of both rolls of the roll pairs complementing each other continuously exclusively in a definite axial position of the rolls. The curved-contour rolls, because they have convex or bulging portions adjacent concave portions, can be referred to as bottle rolls.
This rolling mill stand is described in German patent DE-PS No. 30 38 865. It has the advantage that the form of the roll gap and thus the rolled strip cross section may be modified exclusively by axially shifting the rolls provided with the curved contour and the roll force distribution changed without problems. The form of the roll gap and thus the cross section of the rolled strip being rolled can be influenced by even slight axial shifting of the rolls having the curved contour, and without particular concern for locating the shiftable rolls with respect to the rolled strip width.
Not only is it possible to use the features according to German Patent DE-PS No. 30 38 865 in rolling mills with supporting and/or intermediate rolls, but also they can easily be made a part of a dual rolling mill.
Additional improvements to the rolling mill stand of German Patent DE-PS No. 30 38 865 are provided in German Open Patent Application DE-OS No. 32 13 496. The rolls of several roll pairs of a roll stand have a fitting curved contour on their roll bodies and are axially shiftable opposing each other.
It is possible in a four-high rolling mill to provide both the working rolls and the backup rolls with a curved contour extending over the entire length of the roll body.
In a six-high rolling mill, the intermediate rolls can also have a curved contour extending over the entire length of the roll body.
However, it is also possible in these systems to use backup rolls which are cylindrical, that is whose contour is axially aligned and linear, while the working and intermediate rolls have a curved contour exending over their entire length.
Finally it is also possible in the prior art to provide the roll body of the working roll with a cylindrical contour over its entire length while the backup rolls are provided with curved shapes extending over their entire length.
In practice this kind of rolling mill has been shown to be able to attain an optimum rolled product in a particularly simple way. In using these rolling mills, particularly in a heavy rolling program, pressures between the contacting surfaces on the roll bodies of neighboring rolls under certain definite operating conditions can occur which lie in the critical range. Because the curved contour extends over the entire length of the roll body, an unsymmetrical load distribution occurs with linear load peaks at that end of the roll body which confronts the concave segment of the curved contour with its body edges.
The highest linear load peaks occur in the contacting gap between neighboring rolls during operation of the rolling mill in which a negative shift position of the rolls having the curved body contour relative to the longitudinal half having the concave contour is present and at the same time a positive bending for the roller concerned occurs, when also the bending force acting on the roll is unidirected to the curvature of the contour. Such operating conditions can lead particularly easily to damage to the roll bodies.